Water from double-displacement

Ammonium perchlorate is a colorless, crystalline compound having a density of 1.95 g/mL and a molecular weight of 117.5. It is prepared by a double displacement reaction between sodium perchlorate and ammonium chloride, and is crystallized from water as the anhydrous salt. 

Remember that an acid-base reaction is a double displacement reaction. Therefore, if sulfuric acid and potassium hydroxide are mixed, the positive ions trade places. The hydrogen ions from the sulfuric acid will react with the negative hydroxide ions to form water. Because a hydrogen ion has a charge of + 1 and a hydroxide ion has a charge of -1, they bond in a 1 1 ratio ... 

The neutralization reaction between an acid and a base is a very important double displacement reaction. In a neutralization reaction, water results when an H+ ion from the acid bonds with an OH ion from the base. 

Figure 13 shows the result of the reaction between KI and Pb(N03)2- The products are a yellow precipitate of Pbl2 and a colorless solution of KNO3. From the equation, it appears as though the parts of the compounds just change places. Early chemists called this a double-displacement reaction. It occurs when two compounds in aqueous solution appear to exchange ions and form two new compounds. For this to happen, one of the products must be a solid precipitate, a gas, or a molecular compound, such as water. Water is often written as HOH in these equations. 

Lew is base OH". The complex (or adduct) HSO is formed by the displacement of the proton from the hydroxide ion by the stronger Lewis acid SOj. In this way, the water molecule is thought of as a Lewis adduct formed from H and OH". Even though this fact is not explicitly shown in the reaction, the water molecule exhibits Bransted acidity (not only Lewis basicity). Note that it is easy to tell that this is a displacement reaction instead of just a complex formation reaction because, while there is only one base in the reaction, there are two acids. A complex formation reaction only occurs w ith a single acid and a single base. A double displacement, or metathesis, reaction only occurs with two acids and two bases. 

The double-displacement mechanism with its covalent intermediate can often be distinguished from single displacement reactions by kinetic experiments in which an appropriate nudeophilic spedes is added to reaction solutions of enzyme and substrate and allowed to compete with water for the covalent intermediate. The dependence of initial velocity on the concentrations of substrate and added nucleophile will produce a distinctive kinetic pattern (i.e., ping-pong kinetics). Observation of such a pattern constitutes strong evidence suggesting that the hydrolase under study effects catalysis through a double-displacement mechanism. 

Sometimes a double-displacement reaction has one produa that is insoluble in water. As that produa forms, it emerges, or precipitates, from the solution as a solid. This process is called precipitation, such a reaaion is called a precipitation reaction, and the solid is called the precipitate. For example, when water solutions of calcium nitrate and sodium carbonate are mixed, calcium carbonate precipitates from the solution while the other product, sodium nitrate, remains dissolved. 

These double-displacement reactions have two major features in common. First, two compotmds exchange ions or elements to form new compounds. Second, one of the products is either a compound that will separate from the reaction mixture in some way (commonly as a sohd or gas) or a stable covalent compotmd, often water. 

A neutralization reaction is a double-displacement reaction of an acid and a base. Acids are compounds that can release hydrogen ions bases are com-poxmds that can neutrafize acids by reacting with hydrogen ions. The most common bases are hydroxide and oxide compounds of the metals. Normally, an acid reacts with a base to form a salt and water. Neutrafization reactions occur because of the formation of the very stable covalent water molecule, H2O, from hydrogen and hydroxide ions. 

In this reaction, which is a double-displacement type, the from the acid combines with the OH from the base to form water. The ionic compound must be composed of the other two ions, and Br . We determine the formula of the ionic compound to be KBr from the fact that K is a -l-l cation and Br is a -1 anion. The final balanced equation is... 

Effect of salt type and concentration The ionic strength of the aqueous solution in eontaet with a reverse micelle phase affects protein partitioning in a number of ways [18,23]. The first is through modification of electrostatic interactions between the protein surface and the surfaetant head groups by modifieation of the eleetrieal double layers adjacent to both the eharged inner mieelle wall and the protein surface. The second effect is to salt out the protein from the mieelle phase because of the inereased propensity of the ionie speeies to migrate to the micelle water pool, reduee the size of the reverse mieelles, and thus displace the protein. 

---